A switched reluctance motor is a synchronous motor that has wound field coils as in a DC motor for its stator windings. However, the switched reluctance motor has no permanent magnets attached. The motor is doubly salient with phase coils mounted around diametrically opposite stator poles. Energisation of a phase of the coil windings will lead to an armature moving into alignment with the stator poles, thereby minimising the reluctance of a magnetic path and producing a torque to drive the armature. In order to achieve full translation of the armature, the coil windings must be energised in a predetermined sequence.
A typical linear switched reluctance motor topology is a unipolar current-driven device. An example of such a motor is disclosed in U.S. Pat. No. 6,078,114 entitled “Method and Apparatus for Vibration Reduction/Control in a Variable Reluctance Linear Motor” wherein a variable reluctance linear motor is described which has a stator, and an armature which is mounted so as to be movable along the length of the stator. Another example is U.S. Pat. No. 6,624,538 entitled “Variable Reluctance Motor with Improved Tooth Geometry” which describes a variable reluctance motor with motor and stator cores comprising base members and a plurality of adjacent tooth members having unique tooth geometries.
The aforesaid prior art documents disclose the traditional approach of obtaining continuous magnetomotive bidirectional forces in a linear switched reluctance motor. This approach differs from a traditional servo motor in that the currents which are provided to three different phases of the motor are non-linear. In addition, the phase inductance variation has a highly non-linear relationship with position. This makes its control more demanding, which tends to produce inferior positioning performance as compared to a servo motor drive. A significant drawback to its widespread adoption has been the unique nature of the driver topology which is necessary to achieve accurate positioning performance. Special, tailor-made drives are required, and they tend to be expensive to implement.